Electrosurgical instruments and techniques are widely used in surgical procedures because they generally reduce patient bleeding and trauma associated with cutting operations as compared with mechanical cutting instruments and the like. Conventional electrosurgical technologies may be classified as being monopolar or bipolar. Monopolar techniques rely on external grounding of the patient, where the surgical device defines only a single electrode pole. Thus, the electric current must pass through the patient to reach the external grounding pad. Bipolar devices have two electrodes that are located in proximity to one another for the application of current between their surfaces. By being located in proximity to one another, bipolar devices have the advantage that current need not be passed through the body, but rather only between the two electrodes.
Conventional bipolar devices are commonly used to maintain or create hemostasis. Electrosurgical energy passing between the electrode poles and through tissue arranged between them promotes coagulation and thereby reduces bleeding. A historic limitation of these devices has been their inability to cut tissue, which greatly limits their utility.
Recently, RF bipolar generators and tools have been developed that cut tissue through the use of plasma. These systems employ a conductive fluid supply which is converted to a plasma ‘bubble ’ on a portion of the electrode tip through the application of RF electrosurgical current. Tissue that contacts the plasma bubble experiences rapid vaporization of its cellular fluid, thereby producing a cutting effect.
Creation of a plasma ‘bubble ’ in the conductive fluid media at the electrode tip requires a very high current density. As such, unlike conventional bipolar instruments, the electrode poles on these devices are not of generally the same size. Rather, one of the poles (generally referred to as the active electrode) is significantly smaller than the other pole (generally referred to as the return electrode). This configuration allows for current density sufficient to form plasma only at the active pole.
When driven at reduced voltage levels that are not sufficient to form and maintain a plasma bubble, these devices can function in a fashion similar to conventional bipolar devices to direct current through a defined area of tissue. Unfortunately, the physical arrangement of the electrodes on these instruments generally limits their capacity for coagulating tissue. In particular, having a small active electrode relative to a large return electrode concentrates current at the small active electrode, which is less than optimal for coagulation where it is desirable to effect a larger lesion or area of tissue coagulation.
It would thus be desirable to provide an improved bipolar electrosurgical instrument that functions effectively as both a cutting and a coagulating instrument.